The use of topical or dermal medicaments has long been utilized in the practice of medicine. In particular, topical anesthetics are commonly administered prior to painful medical procedures such as injections, biopsies, and the application of laser energy for cutaneous procedures such as removal of hair, tattoos, telangiectasias, etc., minor superficial surgeries, and the like.
Several topical anesthetic formulations have been extensively used by the medical field to obtain local anesthesia. These products are known to be effective as topical anesthetics; however, a long onset time, which is the time between the administration of the topical anesthetic and the commencement of the anesthetic effect, are a common limitation of conventional topical anesthetics. To enhance skin penetration of conventional topical anesthetics, it is often recommended that skin having anesthetic applied thereto be covered with an occlusive dressing. Typically, the onset of action for conventional topical anesthetics varies over a range of time, for example from 30 to 90 minutes. This variability in length of onset time leads to delays in the commencement of medical procedures and, because of the very wide variation in onset time, can lead to the premature commencement of procedures and the infliction of unnecessary pain on the patient.
One particular topical anesthetic utilized to suppress or eliminate pain during such procedures is known by the trade name EMLA®. This product is known to be effective as a topical anesthetic; however, EMLA® has a very long onset time, which can range from 45 to 90 minutes and, in some instances, can take even longer. The variability in length of onset time leads to delays in the commencement of medical procedures and, because of the very wide variation in onset time, can lead to the premature commencement of procedures, thereby inflicting unnecessary pain on the patient. EMLA® must also be covered with an occlusive dressing to enhance penetration. Another disadvantage of EMLA® is that one of its two active ingredients, prilocaine, causes vasoconstriction, and so cannot be used before procedures such as IV placement, blood drawing and laser removal of telangiectasias. EMLA is also an opaque cream and as a result decreases the effectiveness of laser procedures.
Accordingly, it would be advantageous and desirable to develop a topically applied, transdermally delivered anesthetic formulation for use before painful procedures such as laser hair removal and skin resurfacing, giving injections, starting IVs, drawing blood, biopsies and minor superficial surgeries which has a more rapid onset time, has less variability in the onset time, does not require occlusion, does not interfere with laser energy penetration into the skin, does not cause vasoconstriction and lastly, permits enhanced penetration of the medicament and thereby allows for a lesser total dosage of pharmaceutically active ingredient. The use of a lesser total dosage thus decreases systemic toxicity. Such a formulation will have a much wider clinical application.
Thus, there exists a need for a vehicle to enhance the transdermal penetration of the active medicament into the deeper epidermis and dermis layers of the skin where the peripheral nerve endings lie, allowing for a fast onset of action. There further exists a need to control the epidermal penetration rate to preclude rapid loss of the active medicament to the systemic circulatory system. With the development of a superior vehicle for transdermal delivery, there also exists rapid onset delivery not only of topical anesthetics to the deeper epidermal and dermis layers, but broad classes of other therapeutics.